The average near-infrared ( K -band ) luminosity of 238 Hipparcos red clump giants is derived and then used to measure the distance to the Galactic center .
These Hipparcos red clump giants have been previously employed as I -band standard candles .
The advantage of the K -band is a decreased sensitivity to reddening , and perhaps also a reduced systematic dependence on metallicity .
In order to investigate the latter , and also to refer our calibration to a known metallicity zero-point , we restrict our sample of red clump calibrators to those with abundances derived from high-resolution spectroscopic data .
The mean metallicity of the sample is [ Fe/H ] = -0.18 dex ( \sigma = 0.17 dex ) .
The data are consistent with no correlation between M _ { K } and [ Fe/H ] , and only weakly constrain the slope of this relation .
The luminosity function of the sample peaks at M _ { K } = -1.61 \pm 0.03 mag .
Next , we assemble published optical and near-infrared photometry for \sim 20 red clump giants in a Baade ’ s Window field with a mean metallicity of [ Fe/H ] = -0.17 \pm 0.09 dex , which is nearly identical to that of the Hipparcos red clump .
Assuming that the average ( V - I ) _ { 0 } and ( V - K ) _ { 0 } colors of these two red clumps are the same , the extinctions in the Baade ’ s Window field are found to be A _ { V } / A _ { I } / A _ { K } = 1.56/0.87/0.15 , in agreement with previous estimates .
We derive the distance to the Galactic center : ( m - M ) _ { 0 } = 14.58 \pm 0.11 mag , or R = 8.24 \pm 0.42 kpc .
The uncertainty in this distance measurement is dominated by the small number of Baade ’ s Window red clump giants examined here .